Electrostatic printing



Filed April 27, I965 INVENTOR. l0i 0.40.5

w ww United States Patent 3,333,572 ELECTROSTATIC PRINTING Roger G.Olden, Trenton, N.J., assignor to Radio Corporation of America, acorporation of Delaware Filed Apr. 27, 1965, Ser. No. 451,266 6 Claims.(Cl. 118637) This invention relates generally to electrostatic printing,and more particularly to improved apparatus for developing anelectrostatic latent image on an electrophotographic recording element.The improved apparatus is particularly useful for developingelectrostatic latent images on a recording element in the form of acontinuous web moving at a relatively high speed.

It has been proposed to develop electrostatic latent images on arecording element in the form of a web by drawing the web through anelectroscopic developer mixture of magnetic particles and tonerparticles. At relatively low speeds (about 1 inch/sec.) of travel of theweb, this method of development is! satisfactory. At relatively higherspeeds (about 24 inches/sec.) of the web, however, the time ofdevelopment is decreased and there is a tendency for the magneticparticles to adhere to the developed recording element. This isespecially true when the ambient humidity is low.

It has also been proposed to increase the speed of conventional, priorart, low-speed developing apparatus to develop recording elements movingat a relatively higher speed, but such apparatus is unsatisfactory athigher speeds because it usually provides excessive agitation andinadequate mixing of the developer mixture. Excessive agitation of someelectroscopic developer mixtures causes their tone-r particles toacquire charges of both positive and negative polarities, instead of acharge of a single desired polarity. Also, excessive agitation of thedeveloper mixture may provide an excessive amount of unwanted tonerdust. I

It is an object of the present invention to provide improved apparatusfor developing an electrostatic latent image on a recording elementmoving at a relatively high speed.

Another object of the present invention is to provide improved apparatusfor removing magnetic particles of an electrostatic developer mixturefrom a recording element moving at a relatively high speed.

A further object of the present invention is to provide improvedapparatus of the type described that is relatively simple in structure,easy to operate, and capable of producing electrostatic prints of goodquality.

Briefly stated, the improved apparatus for developing a latent image onthe surface of an electrophotographic recording element comprises meansfor guiding the recording element along a predetermined path, arotatable brush disposed to apply a developer mixture to the recordingelement during the latters movement, magnetic means disposed to providemagnetic circuits for removing magnetic particles of the developermixture from the recording element, and means including an endless beltto replenish the developer mixture with toner particles as the latterare used. The speed of movement of the recording element is greater thanthe peripheral speed of the brush to provide a wiping action between therecording element and the brush. This is particularly important at highweb speeds because, if the brush were moving faster than the recordingelement, the centrifugal force acting on the magnetic and tonerparticles would cause them to fly off and thus make them useless for thepurpose intended. The peripheral speed of the endless belt is less thanthat of the brush to provide a good wiping action between the belt andthe brush.

The novel features of the present invention both as to its organizationand operation, as well as additional obice jects and advantages thereof,will be more readily understood from the following description, whenread in connection with the accompanying drawing, the single figure ofwhich is a partly schematic, cross-sectional, side elevational view ofdeveloping apparatus according to one embodiment of the presentinvention.

Referring now to the drawing, there is shown developing apparatus 10 fordeveloping an electrostatic latent image on the outer surface 11 of anelectrostatic recording element 12. The recording element 12 maycomprise a photoconductive layer on a suitable backing sheet, and anelectrostatic latent image may be formed on the photoconductive layer byany suitable means known in the art. An example of a suitable recordingelement 12 and means for producing an electrostatic image thereon aredescribed in RCA Review, December 1954, volume XV, No. 4.

The developing apparatus 10 comprises a drum 14 rotatably disposed on astationary hollow shaft 16. The drum 14 is coupled to the stationaryshaft 16, preferably by roller bearings (not shown), in a manner wherebythe drum is free to rotate about the stationary shaft 16. The recordingelement 12 is disposed about, and in contact with, the outer peripheryof the drum 14 and is adapted to rotate the drum 14, in the directionindicated by the arrow 18, when the recording element 12 is moved, inthe directions of the arrows 17 and 19, by driving means (not shown)associated with the recording element 12.

An electromagnet 20 is fixed to the stationary shaft 16 within the drum14 by any suitable means. The electromagnet 20 has a pair of pole pieces22 and 24- whose opposite edges are disposed adjacent to the innerperiphery of the drum 14 and which extend parallel to the axis of thedrum 14. When a D.-C. voltage is applied between leads 26 and 28 of acoil 30- of the electromagnet 20, the pole pieces 22 and 24 becomemagnetic poles of opposite polarities. Under these conditions, magneticcircuits 32 and 34, indicated by dashed lines, are set up between theedges of the pole piece 22 and 24 when the electromagnet 20 isenergized. The electromagnet leads 26 and 28 are brought outside of thedrum 14 through a bore 36 in the shaft 16.

Means are provided to apply a developer mixture 38 of toner particles 40and magnetic particles 41, such as iron filings, for example. Suitabledeveloping mixtures for use with the apparatus 10' are described in US.Patent 2,986,521 for Reversal Type Electrostatic Developer Powder,issuedMay 30, 196-1. The developer mixture 38 is disposed in a trough42, and rotatable cylindrical brush 44 is disposed in the developermixture 38.

The brush 44 comprises a rod 46 about which a strip 48 of Nylon velouris wound. The nap 50 of the brush 44 should be at least 4 inch long. Thebrush 44 is mounted for rotation so that its nap 50 brushes against thesurface 11 of the recording element 12 and applies the developer mixture38 to the latent image on the recording element 12 to develop the latentimage. The axes of the drum 14 and the brush 44 are substantiallyparallel to each other, and the brush 44 is rotated, in a directionindicated by the arrow 52, by a motor 54 coupled to the brush 44 througha gear train 56, so that their tangential motions at their line ofmutual contact are in the same direction.

Means are provided to replenish the developer mixture 38 with tonerparticles that are removed from the developer mixture 38 by thedevelopment of the latent image on the recording element 12. To thisend, a V- shaped container 58 is disposed above an endless belt 60, thelatter being made of a thin rubber-coated fabric and being disposedbetween two rollers 62 and 64 to carry toner particles to the brush 44.The axes of the rollers 62 and 64 are parallel to the axis of the brush44, and the roller 64 is disposed to cause the belt 60 to brush againstthe nap 50 of the brush 44. The width of the belt 60 is coextensive withthat of the brush 44. A vibratory mechanism 66 is connected to thecontainer 58 to agitate the latter and to cause the replenisher tonerparticles 40 to fall through a IOU-mesh screen 68 forming a bottomportion of the container 58. The roller 64 is coupled to the gear train56 to transport the toner particles 40, that have fallen from thecontainer 58 onto the belt 60, to the brush 44. The brush 44 mixes thetoner particles 40 with the developer mixture 38, thus restoring themixture 38 to its original concentration of toner particles. The trough42 extends beneath the belt 60 to catch any toner particles 40 that mayfall from the belt 60.

A pair of spaced-apart rollers 70 and 72 of magnetic material aredisposed adjacent to ends 74 and 76 of the pole pieces 24 and 22,respectively. The rollers 70 and 72 have knurled cylindrical surfaces 80and 82, respectively. The axes of the rollers 70 and 72 are parallel tothe axis of the drum 14, and the rollers 70 and 72 form a part of themagnetic circuit 34 between the ends 74 and 76 of the pole pieces. Thegap 78 between the outer surface 11 of the recording element 12 and theknurled cylindrical surface 80 of the roller 70 is less than thedistance between the outer surface 11 of the recording element 12 andthe end 74 of the pole piece 24. Similarly, the gap 84, between theknurled cylindrical surface 82 of the roller 72 and the surface 11 ofthe recording element 12 is smaller than the distance between the end 76of the pole piece 22 and the surface 11. Under these conditions, anymagnetic particles 41 that may adhere to the surface 11 of the recordingelement 12 are attracted more to the rollers 70 and 72 than to the polepieces 22 and 24. The rollers 70 and 72 are rotated by the motor 54through the gear train 56 and may rotate in either the same direction orin opposite directions. A baffle plate 86 is disposed, by any suitablemeans, adjacent the lower portion of the roller 70 and the upper portionof the roller 72 to prevent magnetic particles, picked up by the roller70, from falling onto the roller 72 and to direct the magnetic particlesonto the belt 60.

The operation of the developing apparatus will now be described: Themotor 54 is energized, thereby rotating the brush 44, the belt 60, andthe magnetic rollers 70 and 72. The vibratory mechanism 66 is alsoenergized. A quantity of developer mixture 38, comprising tonerparticles 40 and magnetic particles 41, is disposed on the belt 60 fromwhere it is taken up by the brush 44, until the brush 44 and the trough42 are fully loaded. When the recording element 12, having anelectrostatic latent image on the outer surface 11 thereof, is movedpast the nap 50 of the rotating brush 44, the latter rotating in thedirection of movement of the recording element 12, a quantity of thedeveloper mixture 38 is brought into contact with the surface 11 todevelop the latent image thereon, Since the peripheral speed of thebrush 44 is different from the speed of movement of the recordingelement 12, a wiping action takes place between the recording element 12and the brush 44, insuring good development of the recording element 12.

In the developing process, magnetic particles 41 tend to adhere to thesurface 11 of the recording element 12. As the developer mixture 38 onthe recording element 12 passes through the magnetic circuit 32, themagnetic particles 41 tend to press the toner particles 40 firmlyagainst the outer surface 11. This is beneficial in producing a crispelectrostatic print with a clean background. Most of the metallicparticles 41 fall from the surface 11 as they emerge from the magneticcircuit 32 and fall onto the belt 60 for return to the developer mixture38. Thus, the magnetic particles 41 need rarely be replenished in thedeveloper mixture 38.

Some metal particles 41, especially at recording element speeds of a fewfeet per second, are carried upward by the recording element 12 into themagnetic circuit 34.

Since the metal particles 41 in passing through the gaps 84 and 78 arenearer to the magnetic rollers 72 and 70 than to the pole piece ends 76and 74, the metal particles 41 are attracted to the rollers 72 and 70and are subsequently returned to the belt 60. Metal particles 41attracted to the roller 70 are eventually dropped onto the bafile 86and, from there, onto the belt 60, the latter returning the metalparticles 41 to the developing mixture 38. Thus, as the rollers 70 and72 rotate, the magnetic force on the metal particles 41 decreases asthey move away from the gaps 78 and '84, and the metal particles 41eventually drop onto the belt which then carries them back to the brush44 and into the trough 42.

At relatively low speeds of travel of the recording element 12, such asfive inches per second, a single roller 72 may be sufficient to cleanexcess metal particles 41 from the recording element 12. At speeds ofseveral feet per second, however, many metal particles 41 are notremoved by a single roller, and the two magnetic rollers and 72 arenecessary. At the higher speeds, it is advantgeous to rotate the roller70 in a direction opposite to that of the roller 72 so that the metalparticles 41 dropped by the roller 70 are not picked up by the roller72.

As the latent images on the outer surface 11 of the recording element 12are developed, toner particles 40 are consumed and removed from thetoner mixture 38. Replenisher toner particles 40 from the container 58,however, are shaken onto the belt 60 and thus carried to the brush 44.The replenisher toner particles 40 are intermingled on the belt 60 withthe metal particles 41 dropped from the rollers 70 and 72 and mixed withthe developer mixture 38 by the brush 44. The peripheral speed of thebelt 60 is relatively much less than that of the brush 44 so that thebrush 44 effectively wipes the toner off the belt 60. The peripheralspeed of the brush 44 may be about one-half the speed of the movement ofthe recording element 12 so as to provide a good wiping action betweenthe brush 44 and the outer surface 11 of the recording element 12.

From the foregoing description, it can be seen that there has beenprovided improved developing apparatus for developing an electrostaticlatent image on a recording element which is moving several feet persecond. Because the brush 44 and the belt 60 have peripheral speeds thatare relatively much slower than the movement of the recording element12, the operation of the apparatus 10 is substantially dust-free, andyet the agitation of the mixture 38 is adequate. While only oneembodiment of the developing apparatus has 'been shown and described,variations in the components of the apparatus, as well as in its methodof operation, all coming within the spirit of this invention, will, nodoubt, suggest themselves to those skilled in the art. Hence, it isdesired that the foregoing shall be considered as illustrative and notin a limiting sense.

What is claimed is:

1. Apparatus for developing a latent image on the surface of therecording element comprising:

record-element guiding means for guiding said recordelement along apredetermined path,

a rotatable br-ush disposed to brush against said surface of saidrecording element during the movement of said recording element alongsaid path,

means disposed beneath said brush for holding a developer mixture oftoner particles and magnetic particles to be applied to said surface bysaid brush to develop said latent image,

an endless belt disposed adjacent said brush,

means to rotate said endless belt and said brush,

means to feed replenisher toner particles to said belt,

magnetic means disposed to create two spaced-apart magnetic circuit-salong said path, each of said circuits traversing said path, and

image on the surface of an electrophotographic recording elementcomprising:

a drum disposed for guiding said record element along a predeterminedpath,

a rotatable brush having a fabric nap disposed to brush against saidsurface of said recording element during the latters movement along saidpath,

a trough disposed beneath said brush for holding an electroscopicdeveloper mixture of toner particles and magnetic particles to beapplied to said surface by said brush to develop said latent image,

an endless belt, having substantially the same width as that of saidbrush, disposed adjacent said brush,

means to rotate said endless beltand said brush at different relativespeeds,

a container for holding replenisher toner particles disposed above saidbelt,

means connected to said container to agitate it, said container beingformed with openings whereby said replenisher toner particles can fallonto said belt when said container is agitated,

magnetic means disposed within said drum to create two spaced-apartmagnetic circuits along said path which are transversely disposedthereto, and

a pair of driven rollers of magnetic material disposed adjacent to saidsurface and forming a part of one of said magnetic circuits forattracting magnetic particles that may adhere to said surface and forcausing them to fall onto said belt for return to said trough.

3. In combination,

a trough for a developer mixture of magnetic particles and tonerparticles,

a rotatable brush having a fabric nap disposed within said trough andadapted to mix said developer mixture when rotated, s

an endless belt disposed between a pair of rollers,

one of said rollers urging said belt against said nap of said brush,

means to feed toner particles disposed to said belt,

a recording-element guiding drum adapted to guide a movingrecording-element web along a path in contact with said nap of saidbrush,

magnetic means fixedly mounted within said drum and providing a pair ofparallel spaced-apart magnetic circuits along said path transverselydisposed to the direction of movement of said web, said drum beingadapted to guide said record-element web past said magnetic circuits,

a magnetic roller disposed in one of said magnetic circuits forattracting magnetic toner particles from said web, and

means connected to said brush, to one of said pair of rollers, and tosaid magnetic roller for rotating said brush, said belt, and saidmagnetic roller.

4. In combination,

a trough for an electroscopic developer mixture of magnetic particlesand toner particles,

a driven rotatable brush having a fabric nap disposed within said troughand adapted to mix said developer mixture when rotated,

an endless belt disposed between a pair of rollers,

one of said rollers urging said belt against said nap of said brush,

a container for replenishing toner particles disposed above said belt,

means connected to said container to agitate it, said container beingformed with openings through which said toner particles can fall ontosaid 'belt, when said container is agitated,

a drum adapted to guide a web recording-element along a predeterminedpath in contact with said nap of said brush, whereby to apply saiddeveloper mixture to said recording-element,

magnetic means fixedly mounted within said drum and providing a pair ofparallel spaced-apart magnetic circuits transversely disposed to saidpath, said drum being disposed to guide said web record-element pastsaid magnetic circuits,

means connected to said brush and to one of said pair of rollers forrotating said brush and said toner belt at dilferent speeds with respectto each other, said drum being adapted to rotate freely,

a pair of magnetic rollers having axes disposed parallel to the axis ofsaid drum and forming a part of one of said magnetic circuits, wherebyto attract any magnetic particles thereto, and

means connected to said pair of magnetic rollers to rotate them, wherebyto cause said attracted magnetic particles to fall therefrom and ontosaid belt for return to said trough.

5. In electrostatic developing apparatus of the type wherein a latentelectrostatic image on a moving web recording-element is developed withtoner particles from an electroscopic developer mixture includingmagnetic particles,

the improvement comprising, in combination,

a rotatable drum disposed to guide said recordingelement web along apredetermined path,

a trough for holding said developer mixture,

a rotatable brush disposed within said trough and having a fabric nap incontact with said recording-element web to apply said developer mixtureto said latent image when said brush is rotated,

a toner feed belt,

means disposing said belt for rotation with a portion of said belt incontact with said nap of said brush,

a container for replenisher toner particles disposed above said belt,

means to agitate said container, said container having openings thereinthrough which said replenisher toner particles can fall onto said beltwhen said con- Itainer is agitated,

magnetic means disposed within said drum for providing two spaced-apartmagnetic circuits along said path,

at least one magnetic roller disposed adjacent to said drum and forminga part of one of said magnetic circuits, and

means to rotate said brush, said belt, and said magnetic roller atdifferent speeds with respect to each other, whereby said developermixture is applied to said recording-element web to develop said latentimage, replenisher toner particles are conveyed to said developermixture to replace toner particles used to develop said latent image,and magnetic particles are removed from said recording-element web bysaid magnetic roller and returned to said belt for mixing with saiddeveloper mixture.

6. In an electrostatic developing apparatus of the type wherein a latentelectrostatic image on a web recordingelement is developed with tonerparticles from an electroscopic mixture including magnetic particles,

the improvement comprising:

a rotatable drum disposed to guiding said recordingelement web along apredetermined path,

a trough for holding said developer mixture,

a rotatable brush disposed within said trough and having a fabric nap incontact with said recording-element web to apply said developer mixtureto said latent image when said brush is rotated,

a toner feed belt having a width substantially co-extensive with that ofsaid brush,

means disposing said belt with a portion thereof in contact with saidnap of said brush,

a container for replenisher toner particles,

means to agitate said container, said container having openings thereinthrough which said replenisher toner particles can fall onto said belt,

magnetic means disposed Within said drum for providing two spaced-apartmagnetic circuits along said path,

a pair of spaced-apart magnetic rollers disposed adjacent to said drumand forming a part of one of said magnetic circuits, and

means connected to said brush, said belt and said rollers to rotate saidbrush, said belt, and said rollers at different speeds with respect toeach other, the peripheral speed of said brush being less than the speed8 of movement of said recordingelement, and the peripheral speed of saidbelt being less than that of said brush, whereby said brush produces awiping action on said recording-element, and said belt pro- 5 duces awiping action on said brush.

References Cited UNITED STATES PATENTS 10 2,061,692 11/1936 Bagley.

2,910,964 11/1959 Stavrakis et a1 118637 3,133,834 5/1964 Sowiak 118-6373,176,652 4/1965 Mott et al. 118637 15 CHARLES A. WILLMUTH, PrimaryExaminer.

PETER FELDMAN, Assistant Examiner.

1. APPARATUS FOR DEVELOPING A LATENT IMAGE ON THE SURFACE OF THERECORDING ELEMENT COMPRISING: RECORD-ELEMENT GUIDING MEANS FOR GUIDINGSAID RECORDELEMENT ALONG A PREDETERMINED PATH, A ROTATABLE BRUSHDISPOSED TO BRUSH AGAINST SAID SURFACE OF SAID RECORDING ELEMENT DURINGTHE MOVEMENT OF SAID RECORDING ELEMENT ALONG SAID PATH, MEANS DISPOSEDBENEATH SAID BRUSH FOR HOLDING A DEVELOPER MIXTURE OF TONER BRUSH FORHOLDING A DEPARTICLES TO BE APPLIED TO SAID SURFACE BY SAID BRUSH TODEVELOP SAID LATENT IMAGE, AN ENDLESS BELT DISPOSED ADJACENT SAID BRUSH,MEANS TO ROTATE SAID ENDLESS BELT AND SAID BRUSH, MEANS TO FEEDREPLENISHER TONER PARTICLES TO SAID BELT, MAGNETIC MEANS DISPOSED TOCREATE TWO SPACED-APART MAGNETIC CIRCUITS ALONG PATH, EACH OF SAIDCIRCUITS TRAVERSING SAID PATH, AND AT LEAST ONE ROLLER OF MAGNETICMATERIAL DISPOSED ADJACENT TO SAID SURFACE AND FORMING A PART OF ONE OFSAID MAGNETIC CIRCUITS FOR ATTRACTING MAGNETIC PARTICLES THAT ARE ONSAID SURFACE AND FOR CAUSING THEM TO FALL ONTO SAID BELT.